In the past, surgical techniques for cataracts and the like have employed a procedure in which the crystalline lens inside the capsule of the eye is extracted through an incision made in the ocular tissue of the cornea (sclera) or the anterior capsule of the lens, then inserting an intraocular lens which replaces the crystalline lens through the incision, to place it within the capsule.
Intraocular lenses employed to date have been single focus lenses lacking a focus adjusting function. A resultant problem has been that while vision recovers after surgery, the ocular function lacks focus adjusting power.
Accordingly, intraocular lenses such as the following have been devised and proposed in the past as intraocular lenses having focus adjusting function.
For example, it has been proposed to use a lens having multiple focal points, such as a bifocal lens or multifocal lens, as an intraocular lens to afford simulated focus adjusting power. However, since such intraocular lenses have simultaneous vision characteristics, quality of vision tends to be poor due, for example, to diminished contrast perception, so satisfactory adjusting function has not yet been achieved.
Patent Citation 1 (JP-A-2004-528135) discloses an intraocular lens composed of a balloon made of a stretchable elastomer which is inserted into the lens capsule, and which adjusts focus through deformation conforming to movement of the capsule. However, owing to the various pressures acting within the lens capsule, it is extremely difficult in practice to precisely control deformation of the balloon placed inside it, and hence to control changes in optical characteristics based on this deformation. The resultant difficulty of ensuring basic vision and stable adjusting power makes the design impractical.
In particular, the intraocular lens taught in Patent Citation 1 promises to afford focus adjusting function through deformation of portions of weakness of the lens occurring as the lens is compressed in the diametrical direction through contraction of the ciliary muscle. However, focus adjustment through deformation of the lens is premised on normal function of the lens capsule, the zonule of Zinn, the ciliary body, and so on, and it is difficult to imagine that the ciliary muscle will be able to exert sufficient force on the inserted intraocular lens subsequent to cataract surgery. Furthermore, during distance vision, the crystalline lens assumes a flattened shape pulled by the zonule of Zinn, whereas during near vision on the other hand, the zonule of Zinn is relaxed through tensing of the ciliary muscle so that the lens recovers its original convex shape. That is, even where contraction through tensing of the ciliary muscle is assumed, it is difficult to imagine that mere relaxation of the zonule of Zinn which connects the ciliary muscle and the crystalline lens will exert compressive force on the lens sufficient to induce curving deformation of the lens as described in Patent Citation 1.
In Patent Citation 2 (JP-A-2003-527898A) it was proposed to insert an intraocular lens having an optical lens disposed in a balloon-shaped elastic member into the lens capsule, and to adjust the focal point through positioning the optical lens forward or backward by deformation of the elastic member based on movement of the lens capsule. With this intraocular lens as well, deformation of the elastic member occurs on the basis of deformation of the lens capsule, and thus as with the balloon discussed previously, there is the problem that it is difficult to control change in optical characteristics with high precision. Furthermore, slight displacement of the optical lens in the anteroposterior direction will by itself produce a change in refractive power of at most no more than about 1 D, so sufficient adjustment function cannot be achieved.
In Patent Citation 3 (JP-A-2001-525220) there was proposed an intraocular lens having a hinge portion disposed on the support member of the optical lens, and affording adjusting power through anteroposterior movement of the optical lens with respect to the optical axis using pressure change of the corpus vitreum when focusing. However, the intraocular lens disclosed in this prior art publication is similar to Patent Citation 2 discussed earlier in that the optical lens merely undergoes slight displacement in the front-back direction, so sufficient adjustment function cannot be achieved. Furthermore, after surgery the lens capsule contracts and fuses to the intraocular lens, and thus there is also a risk that movement of the optical lens will be inhibited by the lens capsule so that sufficient adjustment function is no longer achieved.
Patent Citation 1: JP-A-2004-528135
Patent Citation 2: JP-A-2003-527898
Patent Citation 3: JP-A-2001-525220